Encapsulation is a physio-chemical process by which chemicals, solids, or gases are enclosed in a shell which prevents the capsulate from interacting with the environment or surrounding chemicals. Capsules can be made from many materials, including membranes, polymers, and fibers of various kinds. Most of the capsules are spherical in shape and the diameters range from nanometers to millimeters. Irregular shaped capsules are also feasible, when crystalline solids are encapsulated. The capsulate can also be embedded in the shell matrix of fibers and substrates. The encapsulation enables the capsulate to reach the area of action without being adversely affected by the environment or surrounding chemicals.
The principal reasons for encapsulation include: isolation and protection of the active chemical so that it will not be lost or degraded; separation of incompatible components; increased stability (protection of the encapsulated materials against oxidation or deactivation due to reaction with the environment); controlled release of active agents (sustained steady state release or delayed burst release). Microencapsulation has been used in various fields including agriculture, food, pharmaceuticals, medicines, cosmetics, textiles, electronics, graphics, printing and defense. The active agents may include drugs, enzymes, vitamins, pesticides, flavors, pigments, and self-repairing agent and initiators.
Microencapsulation has been developed over 70 years and to a large extent, is a mature technology widely used in a large array of industries as mentioned above. However, most applications are in a relatively passive environment without active hostile actions, such as a shear actions from oil pumps, sliding surfaces contacts such as ring-liner sliding, or cam-lifter actions or overhead cam bearing etc. in engines. Therefore, the kind of chemical agents that may be encapsulated are limited to relatively pure compounds and mixture of simple chemicals.
In engine lubricant applications, in addition to the severe mechanical sliding actions, the lubricant itself is composed of base oils and additives, creating a complex chemical soup where small particles are dispersed by dispersants, surfaces are cleaned by detergents, and acids are neutralized by, for example, metal sulfonates with micelles of calcium carbonates.
When using polymeric capsules, the mechanical strength and associated properties usually cannot withstand constant shearing, high contact pressures, or combination of high temperatures and pressures such as those encountered in engine lubricant applications. Complex additive compounds (such as a complex mixtures of molecular weights, functional groups, and/or compounds with nanoparticles embedded into the molecular structures) including dispersants, detergents, overbased materials, and antiwear agents have not been successfully encapsulated due to their complexity and charge driven aggregation tendencies. The combination of a hostile chemical environment and a highly stressed mechanical environment typically renders conventional microencapsulation technology ineffective.
There is therefore a need for new encapsulation processes for complex additives for use, for example, in lubricant applications.
The following references may provide background to the present invention: U.S. Pat. Nos. 5,112,541 and 6,330,818 and U.S. Publication Nos. 2010/0297466 and 2014/0087982.